JP2701288B2 - Gear pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gear pump, and particularly to a gear pump suitable for a low-viscosity liquid.

(Prior Art) A hydraulic pump used for a hydraulic device of a vehicle such as a construction vehicle, an agricultural tractor, a forklift, etc. has a simple structure, can be reduced in size and weight, and has severe performance in performance. Gear pumps that can withstand the conditions, in particular, external gear pumps are most often employed. The basic structure of this external gear pump is a simple one that incorporates two gears, a drive gear and a driven gear. The drive gear is integrated with the drive shaft (input shaft) and connected to the output shaft of the power source. When the driving gear rotates, the meshing driven gear rotates, and the two gears suck oil from the suction port and discharge oil from the discharge port. Both side surfaces of these two gears are the side surfaces of the casing, and the tooth tips are also tightly wrapped by the cylindrical portion of the casing, and the internal leakage is kept very small. Although this internal leakage is very small, it is indispensable for lubrication of the sliding part, and the internal leakage cannot be reduced to zero.

To increase the volumetric efficiency of the gear pump, the clearance between the tooth tip of each gear and the inner surface of the casing (tooth clearance) and the clearance between both side surfaces of each gear and the side surface of the casing (hereinafter referred to as side clearance) ) Near zero to minimize the amount of leakage from each gap. In particular, for a low-viscosity liquid, the ratio of the amount of leakage from each gap (the amount of leakage / theoretical discharge amount) increases, and it is indispensable to reduce each of the gaps.

(Problems to be Solved by the Invention) However, in order to make the side clearance close to zero, it is necessary to extremely increase the processing accuracy of each part. The price increase ratio is larger than that, and it becomes very expensive. Further, in consideration of the temperature condition, it is necessary to provide a clearance larger than the difference in thermal expansion of each component. For these reasons, workability and economy have conventionally been given priority over volumetric efficiency, and the volumetric efficiency has been reduced.

As a means of reducing the side clearance, there is a method of pressing the bearing with an elastic member such as a spring or rubber from the back surface of the bearing (an end surface opposite to the gear) in addition to increasing the processing accuracy. It is not possible to adjust the elastic load according to the pressure, and therefore the end face of the bearing is excessively pressed against the gear side surface and burns, causing wear, or the pressing force is too weak, causing an increase in the amount of leakage, etc. There is a problem.

The present invention has been made to solve the above-described problem, and the load for pressing the side surface of the bearing from the back surface of the bearing against the side surface of the gear is changed in accordance with the discharge pressure of the pump to always minimize the side clearance. It is an object of the present invention to provide a gear pump in which the amount of leakage is regulated to increase the volumetric efficiency.

(Means for Solving the Problems) According to the present invention, in order to achieve the above-mentioned object, a suction port is rotated by rotation of two gears housed in a pump casing via a bearing so as to mesh with each other. A pump having a passage (15) for introducing the liquid leaked from the bearing gap and a passage (16) for guiding the introduced liquid to the suction port side of the gear pump for sucking the liquid from the pump and sending the liquid from the discharge port.
A pressure detection chamber (13) having a chamber (13a), a second chamber (13b) having a passage (17) for introducing the discharge pressure of the pump, and one end of the pressure detection chamber (13). Room (13
a), the other end is inserted into the second chamber (13b), and the first chamber (13b) is inserted.
a) a leak amount of liquid from the first chamber (13a) to the suction port having a cross-sectional area that reduces the pressure applied to the back of the bearing of (a) by a certain ratio from the discharge pressure of the second chamber (13b); And a piston (14) for balancing the pressure applied to the rear surface of the bearing and the discharge pressure by the orifice effect of the notch (14c).

(Operation) The liquid leaking from the bearing gap is introduced into the first chamber (13a) and then returned to the pump inlet (2d) through the notch (14c). The internal pressure of the first chamber (13a) becomes the pressure on the back of the bearing. On the other hand, the discharge pressure of the pump is introduced into the second chamber (13b), and the piston (14) has a pressure at which the back pressure of the bearing in the first chamber (13a) is reduced by a fixed rate from the discharge pressure of the pump. So that the notch (14c)
Is adjusted until the discharge pressure and the bearing back pressure are balanced by the orifice effect of the notch. As a result, the pressure on the back side of the bearing is adjusted according to the discharge pressure, and the side clearance is always minimized, thereby increasing the volumetric efficiency of the pump.

Embodiment An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIGS. 1 and 2 show a circumscribed gear pump to which the present invention is applied. The circumscribed gear pump 1 has a casing 2 in which a drive gear 3 and a driven gear 4 are housed, and a drive shaft (input) to which the drive gear 3 is fixed. The shaft 5 and the driven shaft 6 to which the driven gear 4 is fixed are rotatably supported by bearings 7, 7, 8, 8 housed in the casing 2, respectively.
One end of the drive shaft 5 protruding from one side wall 2a of the casing 2 is sealed in a fluid-tight manner by a shaft seal 9, and an end plate 10 is screwed to the other open end of the casing 2 in a fluid-tight manner. The casing 2 is fixed and hermetically sealed. The casing 2 and the end plate 10 form a pump casing.

At the approximate center of the inner surface of the side wall 2a of the casing 2 and the inner surface of the end plate 10, a concave portion 2b facing each end surface of each of the bearings 7, 7, 8 and 8,
10b is formed. On the other hand, a through hole 6a is formed in the shaft core of the driven shaft 6, and communicates the recesses 2b and 10b provided on the end faces of the bearings 7 and 8 on the side opposite to the gear.

A pressure adjusting means 12 is built in the end plate 10, and the pressure adjusting means 12 presses the end faces of the bearings 7, 8 against both side faces of the gears 3, 4 according to the discharge pressure of the gear pump 1. The pressing force is adjusted so that the side clearance between the two is always minimized. The pressure adjusting means 12 includes a pressure detection chamber 13, a piston 14 and a spring 19 which are slidably fitted in the pressure detection chamber 13 in a liquid-tight manner.

The pressure detecting chamber 13 is a concentric and stepped hole, and has a large-diameter low-pressure chamber 13a (first chamber) and a high-pressure chamber 13b (second chamber) communicating with the low-pressure chamber 13a and having a smaller diameter than the low-pressure chamber 13a. 2 with 2 rooms)
It is formed by two chambers. The first chamber and the second chamber are configured such that the pressure of the bearing back pressure introduced into the first chamber is reduced (smaller) by a fixed ratio from the discharge pressure introduced into the second chamber. Set to the cross-sectional area.

The piston 14 has a large-diameter portion 14a that fits into the low-pressure chamber 13a of the pressure detection chamber 13 and a small-diameter portion 14b that fits into the high-pressure chamber 13b, and is formed integrally with an end face of the large-diameter portion 14a. A pressure is applied, and a discharge pressure is applied to the end face of the small diameter portion 14b.

The low-pressure chamber 13a is communicated with the recess 10b by the passage 15,
Further, an annular groove 13c is formed in the upper part of the side wall of the low-pressure chamber 13a, and the annular groove 13c is formed in the end plate 10 and the casing 2a.
The casing 2 communicates with a suction port 2d side of the casing 2 by a passage 16 (FIG. 2) formed in the casing 2. The passage 15 is a passage for introducing the liquid leaked from the bearing gap into each of the recesses 2b and 10b of the casing 2 and the end plate 10 into the low-pressure chamber 13a, and the passage 16 is formed from the bearing gap whose pressure has been adjusted as described later. This is a passage for returning the leaked liquid to the suction port 2d (FIG. 2) side.

The end of the high-pressure chamber 13b is communicated with the end plate 10 and a passage 17 formed in the casing 2 (FIG. 2) to the discharge port 2e side of the casing 2. The passage 17 is a detection hole for guiding the discharge pressure on the discharge port 2e side of the gear pump 1 into the high-pressure chamber 13b.

The piston 14 has a notch 1 on the side of the large diameter part 14a for adjusting the flow rate.
A notch 4c is formed, and the notch 14c is cut in a substantially triangular shape in a tapered shape from the side surface to the end surface as shown in FIG. The notch 14c can communicate with the annular groove 13c, and the opening area with the annular groove 13c changes according to the moving position of the piston 14. Thus, the amount of liquid flowing from the low-pressure chamber 13a through the notch 14c to the annular groove 13c can be adjusted according to the movement position of the piston 14. The notch 14c of the piston 14 is formed into a tapered shape so as to have a flow rate characteristic so that it can easily cope with a change in the amount.

A plug 18 is screwed to the open end of the pressure detection chamber 13 of the end plate 10 in a liquid-tight manner, and the end face of the large-diameter portion 14a of the piston 14 and the plug 18
A spring 19 is contracted between the end face and the end face. When the gear pump 1 stops or the discharge pressure is low, the spring 19 pushes up the piston 14 to fully open the notch 14c,
The low-pressure chamber 13a communicates with the annular groove 13c with a maximum opening area. Also, an O-ring 2 is provided at the end of the small diameter portion 14b of the piston 14.
0 is installed to prevent the high-pressure liquid for pressure detection introduced into the high-pressure chamber 13b from leaking to the low-pressure chamber 13a side, thereby preventing the discharge pressure of the gear pump 1 from decreasing.

 The operation will be described below.

When the gear pump 1 is stopped or when the discharge pressure is low, the third
As shown in the figure, the piston 14 is pushed up by the spring force of the spring 19, and the notch 14c of the piston 14 is fully open, that is, communicates with the annular groove 13c with a maximum opening area. In this state, the low-pressure chamber 13a communicates with the suction port 2d through the notch 14c, the annular groove 13c, and the passage 16, and the low-pressure chamber 13a has the same low pressure as the suction port 2d. The liquid in the gear pump 1 is supplied to both side surfaces of the gears 3 and 4 and each bearing 7,
8, that is, the side clearance, the input shaft 5, and the driven shaft 6
These gears 3, while lubricating between the bearings 7 and 8,
It flows in the bearings 7, 8 toward both ends in a direction away from 4, and flows into the recesses 2 b and 10 b of the casing 2 and the end plate 10.

The liquid flowing into the concave portion 2b of the casing 2 reaches the concave portion 10b of the end plate 10 through the hole 6a passing through the axis of the driven shaft 6, and the liquid in the concave portion 10b flows into the low-pressure chamber 13a through the passage 15. The liquid that has flowed into the low-pressure chamber 13a passes through the notch 14c, the annular groove 13c, and the passage 16 that are fully open, and the suction port 2d (second
(Fig.) As a result, the pressure in the low-pressure chamber 13a, that is, the concave portions 2b and 10b of the casing 2 and the end plate 10 is minimized, and both end surfaces 3a, 3a, 4a and 4a of the gears 3 and 4 and each bearing 7,
The gap between the end faces 7a, 7a, 8a, 8a of the 8, ie, the side clearance, is maximized as shown. In the drawings, the side clearance is exaggerated. Thereby, the inside of the gear pump 1 can be quickly filled with the liquid.

When the gear pump 1 rotates and the discharge pressure rises, the liquid discharged from the gaps (bearing gaps) between the shafts 5 and 6 and the bearings 7 and 8 due to the discharge pressure is discharged on both sides of the gears 3 and 4.
While lubricating the bearing portions, the gears 3 and 4 flow in the bearings 7 and 8 toward both ends in a direction away from both side surfaces thereof,
As described above, it flows into the low-pressure chamber 13a. This low pressure chamber 13a
The liquid inside flows into the annular groove 13c via the notch 14c while pushing up the piston 14. At this time, the flow rate of the liquid is restricted by the orifice effect of the notch 14c and flows from the annular groove 13c to the suction port 2d side.

On the other hand, the discharge pressure of the gear pump 1
), And is introduced into the high-pressure chamber 13b to press the piston 14 downward. Then, the piston 14 stops at a position where the discharge pressure for pressing the piston 14 downward and the bearing back pressure in the low-pressure chamber 13a reach equilibrium. At this time, the pressure in the low-pressure chamber 13a, that is, the pressure in the recesses 2b and 10b of the casing 2 and the end plate 10 is determined by the orifice effect of the notch. That is, the back pressure of each bearing 7, 8 is determined, and each bearing 7, 8 presses both side surfaces 3a, 4a of each gear 3, 4 with each end face 7a, 8a according to the back pressure.
The side clearance between these two is adjusted to the minimum.

When the back pressure of each of the bearings 7 and 8 does not reach the specified pressure at a normal discharge pressure, the piston 14 is pressed downward by the pressure of the high pressure chamber 13b, and the notch 14c is controlled to close. As a result, the flow of the liquid in the low-pressure chamber 13a to the suction port 2d side is reduced, and the pressure in the low-pressure chamber 13a is increased, and the pressure for pressing the rear surfaces of the bearings 7 and 8 is increased. Thus, the clearance between the side surfaces 7a and 8a of the bearings 7 and 8 and the side surfaces 3a and 4a of the gears 3 and 4 is adjusted to be small. This operation continues until the hydraulic pressure in the low-pressure chamber 13a and the discharge pressure in the high-pressure chamber 13b reach equilibrium, and is adjusted so that the side clearance is minimized according to the discharge pressure of the gear pump 1.

Contrary to the above, the discharge pressure of the gear pump 1 is low and the high pressure chamber
When the pressure of 13b becomes lower than the liquid pressure in the low pressure 13a, the piston 14 is pushed upward to increase the opening area of the notch 14c, and accordingly, the liquid in the low pressure chamber 13a flows to the suction port 2d side. Both outflows increase, and the fluid pressure in the low-pressure chamber 13a decreases.
As a result, the back pressure of the bearings 7 and 8 decreases,
4 and the lateral clearance between them increases. This operation continues until the piston 14 reaches equilibrium, and the side clearance is adjusted to a minimum according to the discharge pressure of the gear pump 1. In this way, by automatically adjusting the back pressure of the bearings 7, 8 according to the discharge pressure of the gear pump 1, the gear pump 1
Can always be adjusted to the minimum state. This makes it possible to make the leak amount ratio, particularly the leak amount ratio in the delivery of a low-viscosity liquid, extremely small.

In this embodiment, the case where the pressure adjusting means 12 is provided in the end plate 10 has been described. However, the present invention is not limited to this, and it goes without saying that the pressure adjusting means 12 may be provided on the side wall of the casing 2.

(Effect of the Invention) Since the present invention has been made as described above, it is possible to always adjust the side clearance to a minimum without considering the processing accuracy, the temperature range, and the like, and to apply a load corresponding to the discharge pressure to both sides of the gear. The bearing can be pressed against the surface, and the amount of leakage from the side surface can be made substantially constant regardless of the discharge pressure. In particular, the amount of leakage of low-viscosity liquid can be greatly reduced, and the leakage amount ratio Can be reduced. Furthermore, when the gear pump is not filled with the liquid at the time of starting the gear pump or the like, it is possible to increase the side clearance to avoid metal-to-metal contact between the gear and the bearing, thereby reducing wear. In addition, when the load is changed depending on the liquid quality, the gear, the material of the bearing, and the like, there is an excellent effect that the side surface clearance can be easily adjusted by changing the cross-sectional area ratio of the piston.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a gear pump according to the present invention, FIG. 2 is a sectional view taken along the direction of the arrows II-II in FIG. 1, and FIG. It is a figure showing a state. 1 ... external gear pump, 2 ... casing, 3 ... drive gear, 4 ... driven gear, 5 ... drive shaft, 6 ... driven shaft,
7, 8 ... bearing, 9 ... shaft seal, 10 ... end plate, 13 ...
Hole, 13a …… Low pressure chamber, 13b …… High pressure chamber, 14 …… Piston,
14c ... notch, 15-17 ... passage, 19 ... spring.

Claims (1)

(57) [Claims] 1. A gear pump for sucking liquid from an inlet and discharging from a discharge port by rotation of two gears rotatably and meshed with each other housed in a pump casing via a bearing. A first chamber (13a) having a passage (15) for introducing the leaked liquid and a passage (16) for guiding the introduced liquid to the suction port side of the pump, and a passage (17) for introducing the discharge pressure of the pump. A second chamber (13b) having
A pressure detection chamber (13) having one end and the other end inserted into the first chamber (13a) of the pressure detection chamber (13), and the other end inserted into the second chamber (13b). It has a cross-sectional area that reduces the pressure applied to the back of the bearing by a fixed ratio from the discharge pressure of the second chamber (13b), and adjusts the amount of liquid leakage from the first chamber (13a) to the suction port. A gear pump comprising: a piston (14) having a notch (14c) formed therein and balancing the pressure applied to the back surface of the bearing and the discharge pressure by the orifice effect of the notch (14c).